In the past, efforts have been made to provide full range stereophonic sound in enclosures that are small and compact. The compact size is desirable for a multitude of home, automotive and commercial applications. However, the development trends in producing stereophonic sound in this environment have focused on small but separate enclosures for the speakers providing the separate stereo channels. Further, the separate, small enclosures for full range audio have had relatively limited performance in the bass frequency region. Thus, the bass range signals are typically separated and directed to a third enclosure dedicated and designed to enhance bass performance. These enclosures are sometime referred to as subwoofer satellites. Because humans do not readily perceive the direction of sound below around 500 Hz, the use of a single subwoofer satellite in monaural configuration is typically provided.
One known technique for improving bass response in larger systems, such as subwoofer satellites, is the positioning of opposing loudspeakers at opposite ends of a hollow cylindrical enclosure so that the loudspeakers enclosed and are mechanically coupled by a volume of air. As developed more fully below, the loudspeakers can be driven by in phase electric signals to produce a mechanically out of phase response. A push-pull effect is achieved in the bass frequency region, whereby the loudspeakers are acoustically in phase, and the resulting sound waves augment each other in the bass frequency region for increased sound intensity.
Because of the increased bass performance, the opposing speaker configurations have been directed to relatively large loudspeakers having diameters greater than six inches. Additionally, these constructions have traditionally been improved for bass region performance by stiffening the enclosure, resulting in an enclosure response with a resonant frequency well above the bass frequency range in which the loudspeakers perform. Hence, the interference by vibration of the enclosure at its resonant frequency is avoided by the limited range of the loudspeakers.
It would be desirable to obtain the benefits of the bass region performance of an opposing loudspeaker enclosure in a compact size capable of stereophonic full bandwidth audio.